Acoustics: an essential requirement of education
Effective oral communication in the field of education, and therefore in the learning process, is closely linked to the room used and the conditions it provides.
Caruso Acoustic has always considered the education sector to be a strategic area for the key principles of its company philosophy, as well as a laboratory for its own research and development sector for its products. Consequently, the company offers highly functional and aesthetic acoustic correction solutions for educational environments.
The acoustic performance of a classroom is an integral part of any quality planning.
The link between productivity and reverberation time
How does productivity change in classrooms where there is no guarantee of suitable acoustic comfort?
Certain studies have shown how students’ margins of error can vary by over 15% in a room where the reverberation time produces a sound above 60 dB. While below 55 dB this percentage falls dramatically to 4.3%.
The clarity of sound perception is closely linked to the duration of the “sound reverberation” in a room, which is usually measured according to its “reverberation time”. For rooms used for education, the contribution towards the reverberation must ensure that a compromise is established so that it helps to reinforce the direct sound. Excessive reverberation and high levels of background noise reduce speech intelligibility.
Therefore, the optimum reverberation time in a room used for listening to others talking is represented by the right compromise between achieving a sufficient level of sound to be effortlessly heard in all corners of the room and making sure that there are no blurred syllables in speech.
The acoustic quality of a room: the materials
The choice of materials for achieving suitable acoustic comfort must aim to reach the optimum reverberation time depending on the intended use of the room. In fact, by correctly applying sound-absorbing materials, it will reduce sound reverberation and absorb energy from unwanted reflections as well as background noise.
With this in mind, the acoustic design of a classroom aims to ensure that the person speaking is as comprehensible as possible. When working to correct the acoustics of a classroom, we must apply different types of materials so that the whole range of the frequencies concerned is absorbed. What’s more: targeted distribution of the acoustic absorption in the room must be planned to guarantee that the same quality of sound can be heard in every corner of the room.
Schools represent a very important area of regulatory application, where different acoustic parameters come into play that must be taken into consideration, given that they can have a considerable impact on the quality of teaching. Speech intelligibility is therefore a fundamental and indispensable requirement.
In 2004, Germany issued DIN 18041:2004-05, a regulation stipulating the optimum acoustic parameters for venues used for education and other activities. This regulation set out the parameters for determining the optimum RT depending on the activity and the volume. Particular attention was also paid to the parameters to be considered for people with hearing disabilities and non-native speakers.
The RT is the first factor to be examined to improve speech intelligibility, but on its own it is not enough to ensure the best results. Different factors which affect perfect speech intelligibility must be taken into account, such as the STI (Speech Transmission Index) and the %ALCONS.
STI measures intelligibility on a scale between 0 (completely incomprehensible) and 1 (perfect intelligibility)
ALCONS expresses the loss of articulation of consonants, with lower values being associated with greater intelligibility. For learning environments the value must be at least 5% or lower.
C50 expresses the clarity of speech (used in particular in Germany) and indicates the sound energy relationship over the first and subsequent 50 ms.
For example we consider a classroom of 108 sqm for a volume of 409 cubic meter and 91 bench places.
Materials on the classroom: plaster on walls and ceiling, parquet on floor, wood on doors.
On occupied classroom, the estimated Reverberation time of 1,73 s for the average 250-2000 Hz is too much high for teaching.
We could obtain an excellent results by applying optimally the Silente M absorbers as illustrated on the picture.
The panels are fitted onto the ceiling in a U-shaped arrangement with the base facing the back wall. Other panels are fixed to the back wall.
By comparing the data from before and after the acoustic improvements in an empty room, we can see a considerable improvement in the reverberation time. While in an occupied room the average RT will change from 500-1000 Hz at 0.59 s to a value of 0.51 s.
Consequently, we also achieve a considerable improvement in the parameters that define speech intelligibility, such as the STI and the ALCONS.
The STI changes from a value of 0.53-0.55, which represents normal conditions, to a value of 0.74-0.77, which can be considered excellent.
We can also see an improvement when we look at the other parameter, the %ALCONS, *with nearly excellent values at 3-4 %.
Loss of Consonants
C50 Speech intelligibility
Speech transmission index difference between direct and indirect sound
The square area of the graphs represents the listening area and to the right we find the respective key, while the examined frequency is 1000 Hz and the sound source used is a man’s voice without amplification.
This arrangement is particularly effective and ensures values close to excellent without any amplification.